Integrated circuit boards are typically tested after assembly to ensure that the boards work properly. The tests consist of subjecting selected components or selected component leads to predetermined signals or series of signals and examining the responses of the components individually and as an interconnected functional group.
To perform the tests, the selected components and leads are electrically connected to a tester, which is part of an automatic test system. As depicted in FIG. 1, the automatic test system 10 includes the tester 12 and a tester receiver 14 that provides contacts 13 through which signals produced by the tester 12 are applied, via a fixture 16, to selected leads 17a and test pads 17b of the components 19 on a circuit board 18. The components 19 and the circuit board 18 are together referred to herein as a device-under-test (DUT) 20. The leads 17a and the test pads 17b are referred to collectively herein as leads 17.
The fixture 16 may include, for example, internal wires 15 that are used to connect the leads 17 to particular ones of the tester receiver's contacts 13. The fixture utilizes a bottom plate 16a to make the actual connections with the contacts 13 of the tester receiver. The bottom plate supports a plurality of "nails" 16b that connect by wire wrap or other means to the internal wires 15. The nails 16b are the contacts through which signals that pass through the fixture are applied to and received from the tester receiver 14.
The fixture 16 must be held in electrical contact with both the tester receiver 14 and the DUT 20, such that all signal connections are properly made. In prior known systems, both the tester receiver 14 and the fixture 16 include a set of conventional spring probes 22, which make the physical connections. The probes 22, individually, are relatively expensive. Accordingly, the fixture 16 and the tester receiver 14, which each include thousands of these spring probes, are costly.
The spring probes 22 are included in the fixture 16 to accommodate the varying lengths of the DUT leads 17, in particular, those leads that extend through the circuit board 18. The spring probes 22 in both the fixture 16 and the receiver 14 also accommodate any bending or warping of the DUT 20 and/or the fixture 16 in response to the relatively large applied force that holds the system components in electrical contact, as discussed below. Further, the spring probes 22 wipe, or dean, the ends of the nails 16b and the DUT leads 17.
The force applied to the various components of the system 10 to bring these components into electrical, and thus, physical, contact must be large enough to activate the springs on the thousands of probes 22. This force must also be applied essentially evenly across the DUT 20 and the fixture 16, to activate all of the springs necessary to make the appropriate connections. Typically, a vacuum or a mechanical force of approximately 4 pounds per square inch is required. The machinery to produce such a force is expensive to acquire and to operate. Further, special care must be taken in applying the force, to avoid excessive warping or bending of the system components.
What is needed is a connection mechanism that is less expensive and requires less applied force per square inch. This connection mechanism must accommodate the variations in the lengths of the DUT leads and any bending or warping of the DUT and the fixture.